Following the slaughter of animals for meat, it is necessary to immediately chill the carcasses of the freshly killed animals from the kill temperature to a temperature at which deterioration of the meat is substantially prevented.
One problem encountered during the chilling process is a loss of moisture from the carcasses. As well as causing undesirable condensation on the walls and ceiling of the chill room, moisture loss results in a significant reduction in the end weight of the carcass, up to about three percent, and a corresponding reduction in profit. Loss of moisture also negatively impacts the quality of the end product, particularly in the appearance of the outer portions of the carcass from which most of the moisture is lost.
The problem of moisture loss has been addressed by subjecting the carcasses to rapid chilling by super-cooled, high velocity air. This type of rapid chilling process is known in the art as “quick chill” or “blast chill”. One such process is described in U.S. Pat. No. 4,028,774 (Allan et al.) issued Jun. 14, 1977, and involves passing a carcass through a specially designed enclosure in which it is chilled by circulation of refrigerated air. As described in the Allen et al. patent, the quick chill process causes the formation of a thin frozen crust on the outer surface of the carcass, thus preventing deterioration of the inner portions of the carcass as it is cooled, and also reducing the moisture loss from the carcass to a relatively low level.
Although the cooling achieved by the quick chill process is relatively rapid, the quick chill process requires a significant period of time to achieve the required temperature reduction and to form a thin frozen crust on the outer surface of the carcass. For example, quick chilling of hog carcasses typically requires about one to two hours.
Based on the belief that there is appreciable loss of carcass weight early in the quick chill process, some have attempted to further reduce moisture loss by freezing the outermost layer of a carcass as rapidly as possible. One such process is described in U.S. Pat. No. 4,325,221 (Grewar) issued Apr. 20, 1982. Grewar discloses rapidly freezing the outermost layer of flesh on a carcass by contacting the carcass with a cryogenic liquid such as liquid nitrogen or liquid carbon dioxide, followed by cooling the carcass throughout by placing it in a mechanically refrigerated cold room under non-thawing conditions.
A similar process is described in U.S. Pat. No. 4,940,599 (Engler et al.), issued Jul. 10, 1990. Engler et al. discloses a process in which carcasses are rapidly chilled by being subjected to a supercold atmosphere, such as a cryogenic fluid, for a brief period of time. According to Engler et al., this results in supercooling of the outermost layer of flesh without the occurrence of crust-freezing. Either immediately before or immediately after the quick chilling of the carcasses, they are sprayed with a fine mist of water, thereby forming a thin ice layer on the outer surface of the carcasses. Once the ice layer is formed, the carcasses are passed into a refrigeration chamber for further cooling.
An improved process for minimizing moisture loss during the chilling process is described in U.S. Pat. No. 6,550,267 (Maxwell et al.), issued on Apr. 22, 2003, and incorporated herein by reference in its entirety. Maxwell et al. discloses a process in which carcasses are sprayed with water early in the quick chill process, preferably at a stage at which the temperature of the outer surface of the carcass is close to 0° C., but before freezing of the outermost layer of flesh occurs. The water freezes to form a protective layer of ice on the carcass. The carcass then continues through the remainder of the quick chill process before entering a refrigeration chamber where cooling is continued and the ice layer is allowed to melt.
Despite the fact that some of the processes described above may provide benefits in terms of reduced moisture loss and improved appearance and quality of the meat product, each of these processes has some disadvantages which limit its usefulness. Therefore, there is a continued need for a chilling process which will further reduce moisture loss and improve product appearance and quality.